linux-kernel - Re: [PATCH v12 11/22] vfio iommu: Add blocking notifier to notify DMA

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Message-ID: <2015af0a-cd66-8092-b075-10a1b434d35c@nvidia.com>
Date:   Tue, 15 Nov 2016 20:41:26 +0530
From:   Kirti Wankhede <kwankhede@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
CC:     <pbonzini@...hat.com>, <kraxel@...hat.com>, <cjia@...dia.com>,
        <qemu-devel@...gnu.org>, <kvm@...r.kernel.org>,
        <kevin.tian@...el.com>, <jike.song@...el.com>,
        <bjsdjshi@...ux.vnet.ibm.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 11/22] vfio iommu: Add blocking notifier to notify
 DMA_UNMAP


>> @@ -854,15 +857,29 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>  		if (dma->task->mm != current->mm)
>>  			break;
>>  		unmapped += dma->size;
>> +
>> +		mutex_unlock(&iommu->lock);
>> +		if (iommu->external_domain && !RB_EMPTY_ROOT(&dma->pfn_list)) {
>> +			struct vfio_iommu_type1_dma_unmap nb_unmap;
>> +
>> +			nb_unmap.iova = dma->iova;
>> +			nb_unmap.size = dma->size;
>> +			blocking_notifier_call_chain(&iommu->notifier,
>> +						    VFIO_IOMMU_NOTIFY_DMA_UNMAP,
>> +						    &nb_unmap);
>> +
>> +			if (WARN_ON(!RB_EMPTY_ROOT(&dma->pfn_list)))
>> +				goto unmap_exit;
>> +		}
>> +		mutex_lock(&iommu->lock);
> 
> Why are the mutexes pushed out so far, we are referencing way too much
> stuff outside of the mutex here.  The notifier head has its own
> semaphore, so we should be able to squeeze the mutex opening to just
> around the notifier call, in which case we only worry about the iommu
> itself going way.
> 

Right. Updating.

Thanks,
Kirti